Re: [RFC PATCH v6 7/9] thermal: introduce the Power Allocator governor

[Eduardo Valentin]

Javi,

Minor items as follows..

On Fri, Dec 05, 2014 at 07:04:18PM +0000, Javi Merino wrote:
> The power allocator governor is a thermal governor that controls system
> and device power allocation to control temperature.  Conceptually, the
> implementation divides the sustainable power of a thermal zone among
> all the heat sources in that zone.
> 
> This governor relies on "power actors", entities that represent heat
> sources.  They can report current and maximum power consumption and
> can set a given maximum power consumption, usually via a cooling
> device.
> 
> The governor uses a Proportional Integral Derivative (PID) controller
> driven by the temperature of the thermal zone.  The output of the
> controller is a power budget that is then allocated to each power
> actor that can have bearing on the temperature we are trying to
> control.  It decides how much power to give each cooling device based
> on the performance they are requesting.  The PID controller ensures
> that the total power budget does not exceed the control temperature.
> 
> Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
> Cc: Eduardo Valentin <edubezval@xxxxxxxxx>
> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
> Signed-off-by: Javi Merino <javi.merino@xxxxxxx>
> ---
>  Documentation/thermal/power_allocator.txt | 196 ++++++++++++
>  drivers/thermal/Kconfig                   |  15 +
>  drivers/thermal/Makefile                  |   1 +
>  drivers/thermal/power_allocator.c         | 511 ++++++++++++++++++++++++++++++
>  drivers/thermal/thermal_core.c            |   7 +-
>  drivers/thermal/thermal_core.h            |   8 +
>  include/linux/thermal.h                   |  40 ++-
>  7 files changed, 774 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/thermal/power_allocator.c
> 
> diff --git a/Documentation/thermal/power_allocator.txt b/Documentation/thermal/power_allocator.txt
> index d3bb79050c27..23b684afdc75 100644
> --- a/Documentation/thermal/power_allocator.txt
> +++ b/Documentation/thermal/power_allocator.txt
> @@ -1,3 +1,172 @@
> +Power allocator governor tunables
> +=================================
> +
> +Trip points
> +-----------
> +
> +The governor requires the following two passive trip points:
> +
> +1.  "switch on" trip point: temperature above which the governor
> +    control loop starts operating.
> +2.  "desired temperature" trip point: it should be higher than the
> +    "switch on" trip point. It is the target temperature the governor
> +    is controlling for.
> +
> +PID Controller
> +--------------
> +
> +The power allocator governor implements a
> +Proportional-Integral-Derivative controller (PID controller) with
> +temperature as the control input and power as the controlled output:
> +
> +    P_max = k_p * e + k_i * err_integral + k_d * diff_err + sustainable_power
> +
> +where
> +    e = desired_temperature - current_temperature
> +    err_integral is the sum of previous errors
> +    diff_err = e - previous_error
> +
> +It is similar to the one depicted below:
> +
> +                                      k_d
> +                                       |
> +current_temp                           |
> +     |                                 v
> +     |                +----------+   +---+
> +     |         +----->| diff_err |-->| X |------+
> +     |         |      +----------+   +---+      |
> +     |         |                                |      tdp        actor
> +     |         |                      k_i       |       |    get_actual_power()
> +     |         |                       |        |       |        |     |
> +     |         |                       |        |       |        |     | ...
> +     v         |                       v        v       v        v     v
> +   +---+       |      +-------+      +---+    +---+   +---+   +----------+
> +   | S |-------+----->| sum e |----->| X |--->| S |-->| S |-->|power     |
> +   +---+       |      +-------+      +---+    +---+   +---+   |allocation|
> +     ^         |                                ^             +----------+
> +     |         |                                |                |     |
> +     |         |        +---+                   |                |     |
> +     |         +------->| X |-------------------+                v     v
> +     |                  +---+                               granted performance
> +desired_temperature       ^
> +                          |
> +                          |
> +                      k_po/k_pu
> +
> +Sustainable power
> +-----------------
> +
> +An estimate of the sustainable dissipatable power (in mW) should be
> +provided while registering the thermal zone.  This estimates the
> +sustained power that can be dissipated at the desired control
> +temperature.  This is the maximum sustained power for allocation at
> +the desired maximum temperature.  The actual sustained power can vary
> +for a number of reasons.  The closed loop controller will take care of
> +variations such as environmental conditions, and some factors related
> +to the speed-grade of the silicon.  `sustainable_power` is therefore
> +simply an estimate, and may be tuned to affect the aggressiveness of
> +the thermal ramp.  For reference, this is 2000mW - 4500mW depending on
> +screen size (4" phone - 10" tablet).

I would rephrase the example as:
'For reference, the sustainable power of a 4" phone is typically 2000mW,
while on a 10" table is around 4500mW (may vary depending on screen
size).

> +
> +If you are using device tree, do add it as a property of the
> +thermal-zone.  For example:
> +
> +	thermal-zones {
> +		soc_thermal {
> +			polling-delay = <1000>;
> +			polling-delay-passive = <100>;
> +			sustainable-power = <2500>;
> +			...
> +
> +If you use platform code to register your thermal zone instead, pass a
> +`thermal_zone_params` that has a `sustainable_power`.  If you weren't
> +passing any `thermal_zone_params`, then something like this will do:
> +
> +	static const struct thermal_zone_params tz_params = {
> +		.sustainable_power = 3500,
> +	};
> +
> +and then pass `tz_params` as the 5th parameter to
> +`thermal_zone_device_register()`
> +
> +k_po and k_pu
> +-------------
> +
> +The implementation of the PID controller in the power allocator
> +thermal governor allows the configuration of two proportional term
> +constants: `k_po` and `k_pu`.  `k_po` is the proportional term
> +constant during temperature overshoot periods (current temperature is
> +above "desired temperature" trip point).  Conversely, `k_pu` is the
> +proportional term constant during temperature undershoot periods
> +(current temperature below "desired temperature" trip point).
> +
> +These controls are intended as the primary mechanism for configuring
> +the permitted thermal "ramp" of the system.  For instance, a lower
> +`k_pu` value will provide a slower ramp, at the cost of capping
> +available capacity at a low temperature.  On the other hand, a high
> +value of `k_pu` will result in the governor granting very high power
> +whilst temperature is low, and may lead to temperature overshooting.
> +
> +The default value for `k_pu` is:
> +
> +    2 * sustainable_power / (desired_temperature - switch_on_temp)
> +
> +This means that at `switch_on_temp` the output of the controller's
> +proportional term will be 2 * `sustainable_power`.  The default value
> +for `k_po` is:
> +
> +    sustainable_power / (desired_temperature - switch_on_temp)
> +
> +Focusing on the proportional and feed forward values of the PID
> +controller equation we have:
> +
> +    P_max = k_p * e + sustainable_power
> +
> +The proportional term is proportional to the difference between the
> +desired temperature and the current one.  When the current temperature
> +is the desired one, then the proportional component is zero and
> +`P_max` = `sustainable_power`.  That is, the system should operate in
> +thermal equilibrium under constant load.  `sustainable_power` is only
> +an estimate, which is the reason for closed-loop control such as this.
> +
> +Expanding `k_pu` we get:
> +    P_max = 2 * sustainable_power * (T_set - T) / (T_set - T_on) +
> +        sustainable_power
> +
> +where
> +    T_set is the desired temperature
> +    T is the current temperature
> +    T_on is the switch on temperature
> +
> +When the current temperature is the switch_on temperature, the above
> +formula becomes:
> +
> +    P_max = 2 * sustainable_power * (T_set - T_on) / (T_set - T_on) +
> +        sustainable_power = 2 * sustainable_power + sustainable_power = 
> +        3 * sustainable_power
> +
> +Therefore, the proportional term alone linearly decreases power from
> +3 * `sustainable_power` to `sustainable_power` as the temperature
> +rises from the switch on temperature to the desired temperature.
> +
> +k_i and integral_cutoff
> +-----------------------
> +
> +`k_i` configures the PID loop's integral term constant.  This term
> +allows the PID controller to compensate for long term drift and for
> +the quantized nature of the output control: cooling devices can't set
> +the exact power that the governor requests.  When the temperature
> +error is below `integral_cutoff`, errors are accumulated in the
> +integral term.  This term is then multiplied by `k_i` and the result
> +added to the output of the controller.  Typically `k_i` is set low (1
> +or 2) and `integral_cutoff` is 0.
> +
> +k_d
> +---

k_d may be conflicted with Kd  (capacitance) of the cooling device power API.

Is it possible to change / rename either one of them?

> +
> +`k_d` configures the PID loop's derivative term constant.  It's
> +recommended to leave it as the default: 0.
> +
>  Cooling device power API
>  ========================
>  
> @@ -25,3 +194,30 @@ milliwatts.
>  
>  Calculate a cooling device state that would make the device consume at
>  most @power mW.
> +
> +Cooling device weights
> +----------------------
> +
> +Weights are a mechanism to bias the allocation between cooling
> +devices.  They express the relative power efficiency of different
> +cooling devices.  Higher weight can be used to express higher power
> +efficiency.  Weighting is relative such that if each cooling device
> +has a weight of one they are considered equal.  This is particularly
> +useful in heterogeneous systems where two cooling devices may perform
> +the same kind of compute, but with different efficiency.  For example,
> +a system with two different types of processors.
> +
> +Weights shall be passed as part of the thermal zone's
> +`thermal_bind_parameters`.
> +
> +Limitations of the power allocator governor
> +===========================================
> +
> +The power allocator governor's PID controller works best if there is a
> +periodic tick.  If you have a driver that calls
> +`thermal_zone_device_update()` (or anything that ends up calling the
> +governor's `throttle()` function) repetitively, the governor response
> +won't be very good.  Note that this is not particular to this
> +governor, step-wise will also misbehave if you call its throttle()
> +faster than the normal thermal framework tick (due to interrupts for
> +example) as it will overreact.
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index f554d25b4399..4496fa5e4a33 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -71,6 +71,14 @@ config THERMAL_DEFAULT_GOV_USER_SPACE
>  	  Select this if you want to let the user space manage the
>  	  platform thermals.
>  
> +config THERMAL_DEFAULT_GOV_POWER_ALLOCATOR
> +	bool "power_allocator"
> +	select THERMAL_GOV_POWER_ALLOCATOR
> +	help
> +	  Select this if you want to control temperature based on
> +	  system and device power allocation. This governor relies on
> +	  power actors to operate.
> +
>  endchoice
>  
>  config THERMAL_GOV_FAIR_SHARE
> @@ -99,6 +107,13 @@ config THERMAL_GOV_USER_SPACE
>  	help
>  	  Enable this to let the user space manage the platform thermals.
>  
> +config THERMAL_GOV_POWER_ALLOCATOR
> +	bool "Power allocator thermal governor"
> +	select THERMAL_POWER_ACTOR
> +	help
> +	  Enable this to manage platform thermals by dynamically
> +	  allocating and limiting power to devices.

I think the config entry deserves a better description, don't you
agree?

> +
>  config CPU_THERMAL
>  	bool "generic cpu cooling support"
>  	depends on CPU_FREQ
> diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> index 39c4fe87da2f..c33904848c45 100644
> --- a/drivers/thermal/Makefile
> +++ b/drivers/thermal/Makefile
> @@ -14,6 +14,7 @@ thermal_sys-$(CONFIG_THERMAL_GOV_FAIR_SHARE)	+= fair_share.o
>  thermal_sys-$(CONFIG_THERMAL_GOV_BANG_BANG)	+= gov_bang_bang.o
>  thermal_sys-$(CONFIG_THERMAL_GOV_STEP_WISE)	+= step_wise.o
>  thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE)	+= user_space.o
> +thermal_sys-$(CONFIG_THERMAL_GOV_POWER_ALLOCATOR)	+= power_allocator.o
>  
>  # cpufreq cooling
>  thermal_sys-$(CONFIG_CPU_THERMAL)	+= cpu_cooling.o
> diff --git a/drivers/thermal/power_allocator.c b/drivers/thermal/power_allocator.c
> new file mode 100644
> index 000000000000..09e98991efbb
> --- /dev/null
> +++ b/drivers/thermal/power_allocator.c
> @@ -0,0 +1,511 @@
> +/*
> + * A power allocator to manage temperature
> + *
> + * Copyright (C) 2014 ARM Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) "Power allocator: " fmt
> +
> +#include <linux/rculist.h>
> +#include <linux/slab.h>
> +#include <linux/thermal.h>
> +
> +#include "thermal_core.h"
> +
> +#define FRAC_BITS 10
> +#define int_to_frac(x) ((x) << FRAC_BITS)
> +#define frac_to_int(x) ((x) >> FRAC_BITS)
> +
> +/**
> + * mul_frac() - multiply two fixed-point numbers
> + * @x:	first multiplicand
> + * @y:	second multiplicand
> + *

If it is a kernel doc, needs a description.

> + * Return: the result of multiplying two fixed-point numbers.  The
> + * result is also a fixed-point number.
> + */
> +static inline s64 mul_frac(s64 x, s64 y)
> +{
> +	return (x * y) >> FRAC_BITS;
> +}
> +
> +enum power_allocator_trip_levels {
> +	TRIP_SWITCH_ON = 0,	/* Switch on PID controller */
> +	TRIP_MAX_DESIRED_TEMPERATURE, /* Temperature we are controlling for */
> +
> +	THERMAL_TRIP_NUM,
> +};
> +
> +/**
> + * struct power_allocator_params - parameters for the power allocator governor
> + * @k_po:	Proportional parameter of the PID controller when overshooting
> + *		(i.e., when temperature is below the target)
> + * @k_pu:	Proportional parameter of the PID controller when undershooting
> + * @k_i:	Integral parameter of the PID controller
> + * @k_d:	Derivative parameter of the PID controller
> + * @integral_cutoff:	threshold below which the error is no longer accumulated
> +			in the PID controller
> + * @err_integral:	accumulated error in the PID controller.
> + * @prev_err:	error in the previous iteration of the PID controller.
> + *		Used to calculate the derivative term.
> + */
> +struct power_allocator_params {
> +	s32 k_po;
> +	s32 k_pu;
> +	s32 k_i;
> +	s32 k_d;
> +	s32 integral_cutoff;
> +	s64 err_integral;
> +	s32 prev_err;
> +};
> +
> +/**
> + * get_actor_weight() - get the weight for the power actor
> + * @tz:		thermal zone we are operating in
> + * @actor:	the power actor
> + *


ditto

> + * Returns: The weight inside the thermal binding parameters of the

s/Returns:/Return:/g


Please run the kernel doc script on your patches and avoid adding
warnings / errors.

> + * thermal zone.  If it could not be found, a default weight of 1 is
> + * assumed.  Weights are expressed as a FRAC_BITS (currently 10-bit)
> + * fixed point integer.
> + */
> +static int get_actor_weight(struct thermal_zone_device *tz,
> +			struct thermal_cooling_device *cdev)
> +{
> +	int i;
> +
> +	for (i = 0; i < tz->tzp->num_tbps; i++)
> +		if (tz->tzp->tbp[i].cdev == cdev)
> +			return tz->tzp->tbp[i].weight;
> +
> +	return int_to_frac(1);
> +}
> +
> +/**
> + * pid_controller() - PID controller
> + * @tz:	thermal zone we are operating in
> + * @current_temp:	the current temperature in millicelsius
> + * @control_temp:	the target temperature in millicelsius
> + * @max_allocatable_power:	maximum allocatable power for this thermal zone
> + *
> + * This PID controller increases the available power budget so that the
> + * temperature of the thermal zone gets as close as possible to
> + * @control_temp and limits the power if it exceeds it.  k_po is the
> + * proportional term when we are overshooting, k_pu is the
> + * proportional term when we are undershooting.  integral_cutoff is a
> + * threshold below which we stop accumulating the error.  The
> + * accumulated error is only valid if the requested power will make
> + * the system warmer.  If the system is mostly idle, there's no point
> + * in accumulating positive error.
> + *
> + * Return: The power budget for the next period.
> + */
> +static u32 pid_controller(struct thermal_zone_device *tz,
> +			unsigned long current_temp, unsigned long control_temp,
> +			u32 max_allocatable_power)
> +{
> +	s64 p, i, d, power_range;
> +	s32 err, max_power_frac;
> +	struct power_allocator_params *params = tz->governor_data;
> +
> +	max_power_frac = int_to_frac(max_allocatable_power);
> +
> +	err = ((s32)control_temp - (s32)current_temp);
> +	err = int_to_frac(err);
> +
> +	/* Calculate the proportional term */
> +	p = mul_frac(err < 0 ? params->k_po : params->k_pu, err);
> +
> +	/*
> +	 * Calculate the integral term
> +	 *
> +	 * if the error is less than cut off allow integration (but
> +	 * the integral is limited to max power)
> +	 */
> +	i = mul_frac(params->k_i, params->err_integral);
> +
> +	if (err < int_to_frac(params->integral_cutoff)) {
> +		s64 i_next = i + mul_frac(params->k_i, err);
> +
> +		if (abs64(i_next) < max_power_frac) {
> +			i = i_next;
> +			params->err_integral += err;
> +		}
> +	}
> +
> +	/*
> +	 * Calculate the derivative term
> +	 *
> +	 * We do err - prev_err, so with a positive k_d, a decreasing
> +	 * error (i.e. driving closer to the line) results in less
> +	 * power being applied, slowing down the controller)
> +	 */
> +	d = mul_frac(params->k_d, err - params->prev_err);
> +	params->prev_err = err;
> +
> +	power_range = p + i + d;
> +
> +	/* feed-forward the known sustainable dissipatable power */
> +	power_range = tz->tzp->sustainable_power + frac_to_int(power_range);
> +
> +	return clamp(power_range, (s64)0, (s64)max_allocatable_power);
> +}
> +
> +/**
> + * divvy_up_power() - divvy the allocated power between the actors
> + * @req_power:	each actor's requested power
> + * @max_power:	each actor's maximum available power
> + * @num_actors:	size of the @req_power, @max_power and @granted_power's array
> + * @total_req_power: sum of @req_power
> + * @power_range:	total allocated power
> + * @granted_power:	output array: each actor's granted power
> + *
> + * This function divides the total allocated power (@power_range)
> + * fairly between the actors.  It first tries to give each actor a
> + * share of the @power_range according to how much power it requested
> + * compared to the rest of the actors.  For example, if only one actor
> + * requests power, then it receives all the @power_range.  If
> + * three actors each requests 1mW, each receives a third of the
> + * @power_range.
> + *
> + * If any actor received more than their maximum power, then that
> + * surplus is re-divvied among the actors based on how far they are
> + * from their respective maximums.
> + *
> + * Granted power for each actor is written to @granted_power, which
> + * should've been allocated by the calling function.
> + */
> +static void divvy_up_power(u32 *req_power, u32 *max_power, int num_actors,
> +			u32 total_req_power, u32 power_range,
> +			u32 *granted_power)
> +{
> +	u32 extra_power, capped_extra_power, extra_actor_power[num_actors];
> +	int i;
> +
> +	if (!total_req_power) {
> +		/*
> +		 * Nobody requested anything, so just give everybody
> +		 * the maximum power
> +		 */
> +		for (i = 0; i < num_actors; i++)
> +			granted_power[i] = max_power[i];
> +
> +		return;
> +	}
> +
> +	capped_extra_power = 0;
> +	extra_power = 0;
> +	for (i = 0; i < num_actors; i++) {
> +		u64 req_range = req_power[i] * power_range;
> +
> +		granted_power[i] = div_u64(req_range, total_req_power);
> +
> +		if (granted_power[i] > max_power[i]) {
> +			extra_power += granted_power[i] - max_power[i];
> +			granted_power[i] = max_power[i];

shouldn't we continue here?

> +		}
> +
> +		extra_actor_power[i] = max_power[i] - granted_power[i];

Do we care when max_power[i] < granted_power[i]? What happens to
(overflowed) extra_actor_power[i]?

> +		capped_extra_power += extra_actor_power[i];
> +	}
> +
> +	if (!extra_power)
> +		return;
> +
> +	/*
> +	 * Re-divvy the reclaimed extra among actors based on
> +	 * how far they are from the max
> +	 */
> +	extra_power = min(extra_power, capped_extra_power);
> +	if (capped_extra_power > 0)
> +		for (i = 0; i < num_actors; i++)
> +			granted_power[i] += (extra_actor_power[i] *
> +					extra_power) / capped_extra_power;
> +}
> +
> +static int allocate_power(struct thermal_zone_device *tz,
> +			unsigned long current_temp, unsigned long control_temp)
> +{
> +	struct thermal_instance *instance;
> +	u32 *req_power, *max_power, *granted_power;
> +	u32 total_req_power, max_allocatable_power;
> +	u32 power_range;
> +	int i, num_actors, ret = 0;
> +
> +	mutex_lock(&tz->lock);
> +
> +	num_actors = 0;
> +	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
> +		if ((instance->trip == TRIP_MAX_DESIRED_TEMPERATURE) &&
> +			cdev_is_power_actor(instance->cdev))
> +			num_actors++;
> +
> +	req_power = devm_kcalloc(&tz->device, num_actors, sizeof(*req_power),
> +				GFP_KERNEL);
> +	if (!req_power) {
> +		ret = -ENOMEM;
> +		goto unlock;
> +	}
> +
> +	max_power = devm_kcalloc(&tz->device, num_actors, sizeof(*max_power),
> +				GFP_KERNEL);
> +	if (!max_power) {
> +		ret = -ENOMEM;
> +		goto free_req_power;
> +	}
> +
> +	granted_power = devm_kcalloc(&tz->device, num_actors,
> +				sizeof(*granted_power), GFP_KERNEL);
> +	if (!granted_power) {
> +		ret = -ENOMEM;
> +		goto free_max_power;
> +	}
> +
> +	i = 0;
> +	total_req_power = 0;
> +	max_allocatable_power = 0;
> +
> +	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> +		int weight;
> +		struct thermal_cooling_device *cdev = instance->cdev;
> +
> +		if (instance->trip != TRIP_MAX_DESIRED_TEMPERATURE)
> +			continue;
> +
> +		if (!cdev_is_power_actor(cdev))
> +			continue;
> +
> +		req_power[i] = cdev->ops->get_actual_power(cdev);


Is this req_power (I read as 'requested power') or actual_power? I would
use the later naming to avoid confusions.

> +		weight = get_actor_weight(tz, cdev);
> +		req_power[i] = frac_to_int(weight * req_power[i]);
> +		total_req_power += req_power[i];

ditto for total_req_power.

> +
> +		max_power[i] = power_actor_get_max_power(cdev);
> +		max_allocatable_power += max_power[i];
> +
> +		i++;
> +	}
> +
> +	power_range = pid_controller(tz, current_temp, control_temp,
> +				max_allocatable_power);
> +
> +	divvy_up_power(req_power, max_power, num_actors, total_req_power,
> +		power_range, granted_power);
> +
> +	i = 0;
> +	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> +		if (instance->trip != TRIP_MAX_DESIRED_TEMPERATURE)
> +			continue;
> +
> +		if (!cdev_is_power_actor(instance->cdev))
> +			continue;
> +
> +		power_actor_set_power(instance->cdev, granted_power[i]);
> +
> +		i++;
> +	}
> +
> +	devm_kfree(&tz->device, granted_power);
> +free_max_power:
> +	devm_kfree(&tz->device, max_power);
> +free_req_power:
> +	devm_kfree(&tz->device, req_power);
> +unlock:
> +	mutex_unlock(&tz->lock);
> +
> +	return ret;
> +}
> +
> +static int check_trips(struct thermal_zone_device *tz)
> +{
> +	int ret;
> +	enum thermal_trip_type type;
> +
> +	if (tz->trips < THERMAL_TRIP_NUM)
> +		return -EINVAL;
> +
> +	ret = tz->ops->get_trip_type(tz, TRIP_SWITCH_ON, &type);
> +	if (ret)
> +		return ret;
> +
> +	if (type != THERMAL_TRIP_PASSIVE)
> +		return -EINVAL;
> +
> +	ret = tz->ops->get_trip_type(tz, TRIP_MAX_DESIRED_TEMPERATURE, &type);
> +	if (ret)
> +		return ret;
> +
> +	if (type != THERMAL_TRIP_PASSIVE)
> +		return -EINVAL;
> +
> +	return ret;
> +}
> +
> +static void reset_pid_controller(struct power_allocator_params *params)
> +{
> +	params->err_integral = 0;
> +	params->prev_err = 0;
> +}
> +
> +static void allow_maximum_power(struct thermal_zone_device *tz)
> +{
> +	struct thermal_instance *instance;
> +
> +	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
> +		u32 max_power;
> +
> +		if ((instance->trip != TRIP_MAX_DESIRED_TEMPERATURE) ||
> +			(!cdev_is_power_actor(instance->cdev)))
> +			continue;
> +
> +		max_power = power_actor_get_max_power(instance->cdev);
> +		power_actor_set_power(instance->cdev, max_power);
> +	}
> +}
> +
> +/**
> + * power_allocator_bind() - bind the power_allocator governor to a thermal zone
> + * @tz:	thermal zone to bind it to
> + *
> + * Check that the thermal zone is valid for this governor, that is, it
> + * has two thermal trips.  If so, initialize the PID controller
> + * parameters and bind it to the thermal zone.
> + *
> + * Return: 0 on success, -EINVAL if the trips were invalid or -ENOMEM
> + * if we ran out of memory.
> + */
> +static int power_allocator_bind(struct thermal_zone_device *tz)
> +{
> +	int ret;
> +	struct power_allocator_params *params;
> +	unsigned long switch_on_temp, control_temp;
> +	u32 temperature_threshold;
> +
> +	ret = check_trips(tz);
> +	if (ret) {
> +		dev_err(&tz->device,
> +			"thermal zone %s has the wrong number of trips for this governor\n",

I would be more specific:
+			"thermal zone %s has wrong trip setup for power allocator\n",


Besides, in 'check_trips' you check more than number of trips.

> +			tz->type);
> +		return ret;
> +	}
> +
> +	if (!tz->tzp || !tz->tzp->sustainable_power) {
> +		dev_err(&tz->device,
> +			"power_allocator: missing sustainable_power\n");
> +		return -EINVAL;
> +	}
> +
> +	params = devm_kzalloc(&tz->device, sizeof(*params), GFP_KERNEL);
> +	if (!params)
> +		return -ENOMEM;
> +
> +	ret = tz->ops->get_trip_temp(tz, TRIP_SWITCH_ON, &switch_on_temp);
> +	if (ret)
> +		goto free;
> +
> +	ret = tz->ops->get_trip_temp(tz, TRIP_MAX_DESIRED_TEMPERATURE,
> +				&control_temp);
> +	if (ret)
> +		goto free;
> +
> +	temperature_threshold = control_temp - switch_on_temp;
> +
> +	params->k_po = tz->tzp->k_po ?:
> +		int_to_frac(tz->tzp->sustainable_power) / temperature_threshold;
> +	params->k_pu = tz->tzp->k_pu ?:
> +		int_to_frac(2 * tz->tzp->sustainable_power) /
> +		temperature_threshold;
> +	params->k_i = tz->tzp->k_i ?: int_to_frac(10) / 1000;
> +	params->k_d = tz->tzp->k_d ?: int_to_frac(0);
> +	params->integral_cutoff = tz->tzp->integral_cutoff ?: 0;
> +
> +	reset_pid_controller(params);
> +
> +	tz->governor_data = params;
> +
> +	return 0;
> +
> +free:
> +	devm_kfree(&tz->device, params);
> +	return ret;
> +}
> +
> +static void power_allocator_unbind(struct thermal_zone_device *tz)
> +{
> +	dev_dbg(&tz->device, "Unbinding from thermal zone %d\n", tz->id);
> +	devm_kfree(&tz->device, tz->governor_data);
> +	tz->governor_data = NULL;
> +}
> +
> +static int power_allocator_throttle(struct thermal_zone_device *tz, int trip)
> +{
> +	int ret;
> +	unsigned long switch_on_temp, control_temp, current_temp;
> +	struct power_allocator_params *params = tz->governor_data;
> +
> +	/*
> +	 * We get called for every trip point but we only need to do
> +	 * our calculations once
> +	 */
> +	if (trip != TRIP_MAX_DESIRED_TEMPERATURE)
> +		return 0;
> +
> +	ret = thermal_zone_get_temp(tz, &current_temp);
> +	if (ret) {
> +		dev_warn(&tz->device, "Failed to get temperature: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = tz->ops->get_trip_temp(tz, TRIP_SWITCH_ON, &switch_on_temp);
> +	if (ret) {
> +		dev_warn(&tz->device,
> +			"Failed to get switch on temperature: %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (current_temp < switch_on_temp) {
> +		tz->passive = 0;
> +		reset_pid_controller(params);
> +		allow_maximum_power(tz);
> +		return 0;
> +	}
> +
> +	tz->passive = 1;
> +
> +	ret = tz->ops->get_trip_temp(tz, TRIP_MAX_DESIRED_TEMPERATURE,
> +				&control_temp);
> +	if (ret) {
> +		dev_warn(&tz->device,
> +			"Failed to get the maximum desired temperature: %d\n",
> +			ret);
> +		return ret;
> +	}
> +
> +	return allocate_power(tz, current_temp, control_temp);
> +}
> +
> +static struct thermal_governor thermal_gov_power_allocator = {
> +	.name		= "power_allocator",
> +	.bind_to_tz	= power_allocator_bind,
> +	.unbind_from_tz	= power_allocator_unbind,
> +	.throttle	= power_allocator_throttle,
> +};
> +
> +int thermal_gov_power_allocator_register(void)
> +{
> +	return thermal_register_governor(&thermal_gov_power_allocator);
> +}
> +
> +void thermal_gov_power_allocator_unregister(void)
> +{
> +	thermal_unregister_governor(&thermal_gov_power_allocator);
> +}
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index c490f262ea7f..4921e084c20b 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1905,7 +1905,11 @@ static int __init thermal_register_governors(void)
>  	if (result)
>  		return result;
>  
> -	return thermal_gov_user_space_register();
> +	result = thermal_gov_user_space_register();
> +	if (result)
> +		return result;
> +
> +	return thermal_gov_power_allocator_register();
>  }
>  
>  static void thermal_unregister_governors(void)
> @@ -1914,6 +1918,7 @@ static void thermal_unregister_governors(void)
>  	thermal_gov_fair_share_unregister();
>  	thermal_gov_bang_bang_unregister();
>  	thermal_gov_user_space_unregister();
> +	thermal_gov_power_allocator_unregister();
>  }
>  
>  static int __init thermal_init(void)
> diff --git a/drivers/thermal/thermal_core.h b/drivers/thermal/thermal_core.h
> index d15d243de27a..b907be823527 100644
> --- a/drivers/thermal/thermal_core.h
> +++ b/drivers/thermal/thermal_core.h
> @@ -85,6 +85,14 @@ static inline int thermal_gov_user_space_register(void) { return 0; }
>  static inline void thermal_gov_user_space_unregister(void) {}
>  #endif /* CONFIG_THERMAL_GOV_USER_SPACE */
>  
> +#ifdef CONFIG_THERMAL_GOV_POWER_ALLOCATOR
> +int thermal_gov_power_allocator_register(void);
> +void thermal_gov_power_allocator_unregister(void);
> +#else
> +static inline int thermal_gov_power_allocator_register(void) { return 0; }
> +static inline void thermal_gov_power_allocator_unregister(void) {}
> +#endif /* CONFIG_THERMAL_GOV_POWER_ALLOCATOR */
> +
>  /* device tree support */
>  #ifdef CONFIG_THERMAL_OF
>  int of_parse_thermal_zones(void);
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index 1155457caf52..b23e019b1761 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -61,6 +61,8 @@
>  #define DEFAULT_THERMAL_GOVERNOR       "fair_share"
>  #elif defined(CONFIG_THERMAL_DEFAULT_GOV_USER_SPACE)
>  #define DEFAULT_THERMAL_GOVERNOR       "user_space"
> +#elif defined(CONFIG_THERMAL_DEFAULT_GOV_POWER_ALLOCATOR)
> +#define DEFAULT_THERMAL_GOVERNOR       "power_allocator"
>  #endif
>  
>  struct thermal_zone_device;
> @@ -255,9 +257,14 @@ struct thermal_bind_params {
>  
>  	/*
>  	 * This is a measure of 'how effectively these devices can
> -	 * cool 'this' thermal zone. The shall be determined by platform
> -	 * characterization. This is on a 'percentage' scale.
> -	 * See Documentation/thermal/sysfs-api.txt for more information.
> +	 * cool 'this' thermal zone. The shall be determined by
> +	 * platform characterization. For the fair-share governor,
> +	 * this is on a 'percentage' scale.  See
> +	 * Documentation/thermal/sysfs-api.txt for more
> +	 * information. For the power_allocator governor, they are
> +	 * relative to each other, see
> +	 * Documentation/thermal/power_allocator.txt for more
> +	 * information.

What happens if we register a thermal zone with relative weights, at
fist the user uses power allocator, but then wants to, for some reason,
use fair share? (or vice-versa).


Can't power allocator use percentages too?

>  	 */
>  	int weight;
>  
> @@ -294,6 +301,33 @@ struct thermal_zone_params {
>  
>  	int num_tbps;	/* Number of tbp entries */
>  	struct thermal_bind_params *tbp;
> +
> +	/*
> +	 * Sustainable power (heat) that this thermal zone can dissipate in
> +	 * mW
> +	 */
> +	u32 sustainable_power;
> +
> +	/*
> +	 * Proportional parameter of the PID controller when
> +	 * overshooting (i.e., when temperature is below the target)
> +	 */
> +	s32 k_po;
> +
> +	/*
> +	 * Proportional parameter of the PID controller when
> +	 * undershooting
> +	 */
> +	s32 k_pu;
> +
> +	/* Integral parameter of the PID controller */
> +	s32 k_i;
> +
> +	/* Derivative parameter of the PID controller */
> +	s32 k_d;
> +
> +	/* threshold below which the error is no longer accumulated */
> +	s32 integral_cutoff;
>  };
>  
>  struct thermal_genl_event {
> -- 
> 1.9.1
> 
>

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